The present invention concerns a feeding method and a feeding chute of a disc chipper fed by means of the gravity. In the pulp and paper industry, a disc chipper is generally used for chipping wood prior to further processing. In a chute fed chipper, the logs are fed along an inclined chute against the blade disc of the chipper. The blade disc rotates around a horizontal or less than 20.degree. inclined axle. The logs slide against the blade disc due to the gravity. Knives are attached to the blade disc in about the direction of the radius, chipping the wood against a stationary counter blade.
The logs encounter the blade disc at a feeding angle which in a chute fed chipper is the angle between the plane of the disc and the plane including the log and perpendicular to the plane of the disc. Test have shown that the quality of chips improves when the feeding angle between the log and the blade disc is decreased. The decreasing of the feeding angle is, however, restricted by the increase of the size of the shearing ellipse of the head of the log, which results in the decrease of the cross section the feeding funnel, if the feeding opening cannot be enlarged at the same time. In addition, practice has proven that smaller feeding angles increase feeding problems of the chipper, as the shearing surface of the log increases and the balancing effect of the gravity on the feed decreases.
The need of enlarging the feeding chute has become the primary problem, which has the effect that the feeding of wood is uncontrollable with the methods of prior art. When small test plants give a good chipping result with the new chipping angles, the quality of the chips with mass production chippers remains significantly lower.
Manufacturers of chippers have developed different feeding methods, which differ from the traditional structure, but these feeding methods, however, have the problem of the restless moving of the logs, especially laterally. The smaller the diameter and the length of the log is, the more lateral movement there is. Slim logs have more space laterally. The length of the logs gets shorter in chipping, so that at the end of chipping the short logs can easily change their direction and turn as much as 90.degree., so that no chips are produced any more.
According to the invention the feeding of the logs into the chipper is provided so that they maintain their feeding direction better. Thus, the problem can be avoided that the chipper would be blocked by transversal logs which have changed their direction, or that when the feeding direction is changed, the size of the chips would be changed and oversized chips would be produced.